This invention relates to an imaging laminate having between a pair of sheets a layer of frangible image-forming substance separable to the respective sheets thereof. More particularly, it relates to a laminar structure particularly adapted to separation of the sheets thereof by mechanical apparatus.
Laminar imaging materials comprising a pair of sheets and a layer of image-forming substance therebetween have been known. For example, laminar thermal imaging materials for the production of images by exposure to heat and separation of the sheets thereof have been described in U.S. Pat. No. 3,924,041 (issued Dec. 2, 1975 to M. Miyayama, et al.); in U.S. Pat. No. 4,157,412 (issued Jun. 5, 1979. to K. S. Deneau); and in International Patent Application No. PCT/US87/03249 of M. R. Etzel (published Jun. 16, 1988 as International Publication No. WO 88/04237). It will be appreciated that an image-forming substance confined between a pair of sheets will be protected against abrasion and rub-off. In addition, a laminar medium can be handled as a unitary structure, thus, obviating the requirement of bringing the respective sheets of a two-sheet imaging medium into proper position in a printer or other apparatus used for imaging of the medium material.
In the aforementioned International Patent Application No. PCT/US87/03249, there are described certain preferred embodiments of a high resolution thermal imaging medium, which embodiments include a porous or particulate image-forming substance in a laminate structure between a pair of sheets. Upon separation of the respective sheets after laser exposure of portions or regions of the medium, a pair of complementary images is obtained.
In U.S. Pat. No. 5,169,475, issued Dec. 8, 1992 to William P. Tobin, there are disclosed certain preferred laminar thermal imaging materials, in the form of individually sized (formatted) thermal imaging laminates. These laminates include a marginal (tab) portion to facilitate separation of the respective sheets of the laminate after a suitable laser scanning exposure. According to a preferred embodiment disclosed therein, the marginal (tab) portion is provided by a score line which severs a marginal portion of one of the sheets and the frangible layer from the remainder of such sheet and layer. Individual (formatted) thermal imaging laminates of the type shown in U.S. Pat. No. 5,169,475 can be stacked in a cassette for supply to a drum or other zone of a printing apparatus and, after thermal exposure, can be separated by an automated delamination device. A suitable such device is described therein.
As is disclosed in U.S. Pat. No. 5,169,475, and in the aforementioned International Application PCT/US87/03249, the image-forming substance of the thermal imaging media thereof is designed to fracture vertically, i.e., in a direction normal to the surface of the layer of image-forming substance. Vertical frangibility of the image-forming layer permits the production of images of desirably high resolution and optical density. The apparatus described in the aforementioned U.S. Pat. No. 5,169,475, in an automated fashion, initiates separation of the sheets of an exposed film unit at the leading (tab) edge thereof and completes the delamination process, for vertical fracture and separation of abutting regions of image-forming substance.
Other apparatus for and methods of delaminating formatted thermal imaging laminates of the type described in U.S. Pat. No. 5,169,475 are described in U.S. Pat. No. 5,169,474, issued Dec. 8, 1992 to Alan M. Binder, for APPARATUS AND METHOD FOR DELAMINATING A COMPOSITE LAMINATE STRUCTURE, in U.S. Pat. No. 5,169,476, issued Dec. 8, 1992 to F. S. Silveira, et al., for APPARATUS AND METHOD FOR DELAMINATION OF A LAMINATE; and in U.S. Pat. No. 5,141,584, issued Aug. 25, 1992 D. F. Schuh, et al., for APPARATUS AND METHOD FOR CONTROLLING THE DELAMINATION OF A LAMINATE.
While various embodiments of mechanical apparatus can be employed to initiate and complete the separation of the sheets of a composite structure having a marginal portion as aforesaid, it has been found that undesired delamination of the composite tab or marginal portion can occur as the result of physical stresses applied by mechanical delamination apparatus to the tab end of the laminate during operation of the delamination process. It will be appreciated that a complete or partial delamination of the composite tab portion, and entanglement of a detached tab portion in the delamination apparatus or larger apparatus of which the delamination apparatus is a part, will be particularly disadvantageous and will hamper the efficient operation of any such apparatus. Accordingly, there will be interest in a laminar composite structure of the aforedescribed type having a tab portion which exhibits a substantial resistance to detachment from the remainder of the structure.